From mboxrd@z Thu Jan 1 00:00:00 1970 From: john clyne Subject: Re: IO transfer limits Date: Wed, 10 Jan 2007 15:47:33 -0800 (PST) Message-ID: <8269227.post@talk.nabble.com> References: <8260533.post@talk.nabble.com> <45A5250E.3020205@cs.wisc.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from www.nabble.com ([72.21.53.35]:54636 "EHLO talk.nabble.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965245AbXAJXrg (ORCPT ); Wed, 10 Jan 2007 18:47:36 -0500 Received: from [72.21.53.38] (helo=jubjub.nabble.com) by talk.nabble.com with esmtp (Exim 4.50) id 1H4nAL-0007Ao-CA for linux-scsi@vger.kernel.org; Wed, 10 Jan 2007 15:47:33 -0800 In-Reply-To: <45A5250E.3020205@cs.wisc.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org What do the different hostX in /sys/class/scsi_host corespond to? There are seven hostX directories, 5 with sg_tablesize set to 128 and two set to 255. Is the implication that the hard limit is 255 * page_size, or is page_size simply the default? Mike Christie wrote: > > john clyne wrote: >> Can anyone give me some guidance on where in the IO stack I might be >> running >> into a 512KB limit on IO transfer sizes to an external FC device? I've >> checked IO scheduler parameter >> (/sys/block//queue/{max_sectors_kb,max_hw_sectors_kb}. Both are set >> to >> 32767. I'm using Qlogic HBAs (qla2312), but I don't see any relevent >> parameters. I'm running RHEL 4.0 with a 2.6.9-34 kernel. Any pointers >> would >> be greatly appreciated. >> > > There are also scatterlist limits. > > /sys/class/scsi_host/hostX/sg_tablesize is a limit for the number of > scatter list entries. For qla2xxx it is 255. > > The scsi layer sets the queue's max_phys_segments to 128 by default. I > thought there was ia scsi compile time option to increase this, but > maybe you have to just modify the SCSI_MAX_PHYS_SEGMENTS define by hand. > > So with the default value and with 4 K pages if you end up getting pages > that cannot be clustered you will end up with 4K * 128. > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- View this message in context: http://www.nabble.com/IO-transfer-limits-tf2953389.html#a8269227 Sent from the linux-scsi mailing list archive at Nabble.com.